Various types of methods and apparatus have been devised in the past for the purpose of inspecting the contents of containers while the containers are in movement. Such systems typically include means such as a conveyor for moving the containers along a path and an inspection station where the contents of each container are inspected using X-ray techniques. One application of such a system is shown in U.S. Pat. No. 3,924,064 issued Dec. 2, 1985 which discloses the use of X-ray inspection equipment for the purpose of inspecting the contents of luggage and baggage.
X-ray inspection systems of the type described above are also well known for use in connection with automatic production line inspection. For example, U.S. Pat. No. 3,958,078 issued May 18, 1986 discloses an X-ray inspection method and apparatus for inspecting the contents of containers such as glass jars filled with food products in which an X-ray image is scanned to provide video signals that are processed in a manner which allows detection of very small foreign particles and without the need for precisely positioning the container at the inspection station. The system disclosed in this prior patent employs a pulsed X-ray source and real time processing which is synchronized to the power line frequency (60 Hz). An X-ray source is pulsed when the presence of a container is detected at the inspection station by a sensor. The resulting X-ray image is processed by an image intensifier which forms a visible image that is converted to a video signal by a camera. The video signal is then analyzed to detect foreign particles or defects in the contents of the container.
Known systems of the type described in the patents mentioned above are limited in their ability to provide container content analysis where the containers are moving at very high speeds through an inspection station, as in a production environment. This limitation is a result of the fact that the resulting X-ray image which is recorded becomes blurred due to rapid movement of the containers. For example, in connection with the container food processing industry, production line rates of between 900 and 1200 or more jars per minute are typical. In other words, approximately 900 to 1200 jars move past an inspection station each minute. Heretofore, it has not been possible to examine the food contents of these jars for foreign particles on a continuous basis at these production rates. Thus, in the past, it was necessary to employ off-line lot sampling techniques to inspect the contents of food containers. Such techniques are, of course, less than completely desirable since foreign particles representing serious health risks may be introduced into those containers that are not inspected.
Many X-ray detection systems, such as the system disclosed in previously-mentioned U.S. Pat. No. 3,958,078, use the cycling of the power line signal to aid in triggering the X-ray source on and off. While this approach has some advantages inasmuch as it allows simplification of the electronic control circuitry, it also has certain disadvantages. One of the most significant disadvantages is that the firing of the X-ray source is partly dependent upon the random phasing of the power line signal. This dependence results in the ultimate image clarity and system speed that can be achieved.
Numerous approaches are employed for turning the X-ray source on and off. A common approach is to switch the X-ray source on by means of a solid-state switching device such as an SCR or a thyristor and allow the X-ray source to be switched off via indirect means. Such indirect means typically uses the cycling of an alternating current source or the natural oscillation of an LRC circuit to reverse bias on an SCR or thyristor that is in series with the X-ray source. In U.S. Pat. No. 3,958,078, the natural oscillations of an LRC circuit are used to reverse-bias a thyristor that is placed in series with the primary winding of the X-ray source step-up transformer. Using indirect means to switch the X-ray source off places much dependence on circuit elements whose tolerances and accuracy are difficult to control. This control problem occurs in both the manufacture of the elements and their use and results in X-ray source timing errors at high operational speeds.
Accordingly, it is the primary object of the present invention to provide a high-speed X-ray inspection system.
A further object of the present invention to provide an X-ray inspection system which uses a direct means for turning off the X-ray source.
Still a further object of the present invention is to provide an X-ray inspection system as described above wherein the firing of the X-ray source is not dependent upon the phasing of an alternating current signal.
Still yet a further object of the present invention is to provide an X-ray inspection system which automatically controls the intensity of the X-ray image.
Yet another object of the present invention is to provide an X-ray inspection system described above which is simple in design and allows the inspection process to be performed fully automatically.
These and further objects of the invention will be made clear or will become apparent during the course of the following description of the preferred embodiments of the present invention.